1. Field of the Invention
The field of the invention relates generally to transmissions, and more particularly the invention relates to continuously variable transmissions.
2. Description of the Related Art
The present invention relates to the field of continuously variable transmissions and includes several novel features and inventive aspects that have been developed and are improvements upon the prior art. In order to provide an infinitely variable transmission, various traction roller transmissions in which power is transmitted through traction rollers supported in a housing between torque input and output disks have been developed. In such transmissions, the traction rollers are mounted on support structures which, when pivoted, cause the engagement of traction rollers with the torque disks in circles of varying diameters depending on the desired transmission ratio.
However, the success of these traditional solutions has been limited. For example, in one solution, a driving hub for a vehicle with a variable adjustable transmission ratio is disclosed. This method teaches the use of two iris plates, one on each side of the traction rollers, to tilt the axis of rotation of each of the rollers. However, the use of iris plates can be very complicated due to the large number of parts that are required to adjust the iris plates during transmission shifting. Another difficulty with this transmission is that it has a guide ring that is configured to be predominantly stationary in relation to each of the rollers. Since the guide ring is stationary, shifting the axis of rotation of each of the traction rollers is difficult.
One improvement over this earlier design includes a shaft about which a driving member and a driven member rotate. The driving member and driven member are both mounted on the shaft and contact a plurality of power adjusters disposed equidistantly and radially about the shaft. The power adjusters are in frictional contact with both members and transmit power from the driving member to the driven member. A support member located concentrically over the shaft and between the power adjusters applies a force to keep the power adjusters separate so as to make frictional contact against the driving member and the driven member. A limitation of this design is the absence of means for generating an adequate axial force to keep the driving and driven members in sufficient frictional contact against the power adjusters as the torque load on the transmission changes. A further limitation of this design is the difficulty in shifting that results at high torque and very low speed situations as well as insufficient means for disengaging the transmission and coasting.
Therefore, there is a need for a continuously variable transmission with an improved power adjuster support and shifting mechanism, means of applying proper axial thrust to the driving and driven members for various torque and power loads, and means of disengaging and reengaging the clutch for coasting.